Probability Calculator

Project Overview

A web application for calculating probabilities using two methods:

1. Combined With: P(A)P(B)
2. Either: P(A) + P(B) – P(A)P(B)

This project was designed to provide a simple and efficient way to calculate probabilities using common probability formulas. The backend is built with Node.js and Express, ensuring a robust and scalable server-side application. The frontend is built with React for a dynamic user interface, Axios for its simplicity and ease of handling HTTP requests, and Tailwind CSS for its utility-first approach to styling.

Key Features

• Probability input validation
• Two calculation methods
• Logging of calculations
• Simple, clean UI

Tech Stack

Node.js, Express, React, TypeScript, Tailwind CSS, Axios, Jest, Winston.

Setup Instructions

Prerequisites

• Node.js (v14+ recommended)
• npm

1. Navigate to the backend directory:

   cd backend

2. Install dependencies:

   npm install

3. Create a .env file in the backend directory and add the following environment variables:

   PORT=5000

4. Start the server:

   npm run dev

   The server will start on http://localhost:5000.

Frontend Setup

1. Navigate to the frontend directory:

   cd frontend

2. Install dependencies:

   npm install

3. Start the frontend application:

   npm start

   The frontend will start on http://localhost:3000.

Running the Application

1. Start the backend server (will run on http://localhost:5000)
2. Start the frontend application (will run on http://localhost:3000)

Testing the API

You can use Postman to test the API endpoints. For example:

1. Open Postman and create a new POST request to http://localhost:5000/api/calculator/combined.

2. Set the request body to JSON and include the following payload:

   {
     "a": 0.5,
     "b": 0.5
   }

3. Send the request and you should receive a response with the combined probability result.

Project Structure

Backend

• server.ts: Main server file.
• routes/calculatorRoutes.ts: Defines API routes.
• controllers/calculatorController.ts: Handles calculator operations.
• services/calculatorService.ts: Core probability calculation logic.
• public: Static files directory.

Frontend

• App.tsx: Main React component.
• components: Directory containing React components.
  • ProbabilityCalculator.tsx: Component for the probability calculator.
• styles: Directory containing CSS files.
  • index.css: Main CSS file.
• setupTests.ts: Setup file for Jest and testing-library configurations.

Why This Setup?

Express Framework: Chosen for its simplicity and flexibility in building server-side applications. React: Component-based architecture for a dynamic UI. Modular Structure: The project is organized into routes, controllers, and services to promote separation of concerns and maintainability. Helmet: Used for setting various HTTP headers to enhance security. CORS: Configured to allow requests from the frontend running on http://localhost:3000. Body-Parser: Middleware to parse incoming request bodies in JSON format. Environment Variables: Managed using dotenv to keep configuration separate from the codebase. Tailwind CSS: For efficient and customizable styling using utility classes. Axios: For making HTTP requests with a simple and promise-based API. Jest: JavaScript testing framework for comprehensive and efficient testing. Winston: For versatile and configurable logging.

Future Improvements

• Add more probability calculation methods.
• Implement user authentication and authorization.
• Improve error handling and logging.
• Enhance the frontend UI/UX.

Conclusion

This project provides a foundational setup for a probability calculator application. The modular structure and use of popular middleware ensure that the application is secure, maintainable, and scalable. The combination of Node.js, Express, and React provides a robust and dynamic platform for building web applications.